Fiber optic-based acoustic sensors represent promising alternatives to conventional electronic sensors. Advantages of fiber optic sensors include high sensitivity, large dynamic range, lightweight and compact size.
Fiber optic sensors may be utilized in various sensing applications, but are particularly useful in undersea applications such as towed array sonar systems employing numerous pressure sensors or hydrophones positioned at predetermined locations along a cable. Here, acoustic waves propagating through a medium such as water are incident on an optical fiber which result in corresponding changes in length and index of refraction of the fiber. Such environmental changes in turn cause changes in one or more characteristics of the light signal, such as a change in the intensity, phase and/or polarization of a light pulse propagating through the fiber. An optical sensor comprising a coil of optical fiber exposed to the medium whose physical parameters are to be measured is often utilized. While phase modulated sensors have been employed for sensing various changes in environmental characteristics, it is also desirable to utilize intensity modulated optical devices. Furthermore, it is often desirable to employ a sensor which is extended in length in order to reduce (e.g. via averaging over the length of the sensor) noise components, such as boundary layer noise.
A method and apparatus for providing an extended optical sensor comprising a series of intensity-based point sensors is highly desired.